1. Field of the Invention
The present invention relates to a dryer section for drying a moving material web, specifically a paper or cardboard web, including several dryer groups that are located one after the other in the direction of web travel.
2. Description of the Related Art
Dryer sections of this type are described, for example in publications U.S. Pat. No. 5,539,999, WO 98/48106 and U.S. Pat. No. 5,673,495.
The present invention provides an improved dryer section including several consecutive dryer groups. Special consideration is given to further optimization of the design of the group separation in the dryer section.
The present invention includes a dryer section for drying a moving material web, specifically a paper or cardboard web, with several dryer groups that are located successively in the direction of web travel. At least one of these is a double row configuration, whereby the material web is continuously supported in at least one transitional zone from a single row dryer group to an immediately following double row dryer group and/or in a transitional zone between two double row dryer groups that are located immediately following each other.
Due to this embodiment, optimum concept geometry for the dryer section results that, among other things, represents savings in the number of rolls and cylinders, including doctors. In addition the overall length of the dryer section can be reduced based on this optimized concept. Improved broke removal is achieved with a rope-free transfer concept. This design concept according to the present invention also permits the installation of auxiliary components, i.e. nozzle devices and/or similar components. In addition, the solution in accordance with the present invention also permits the installation of, for example, web knock-off devices. The result is an optimum arrangement of group separation in the dryer section, and especially an optimization of a respective transition from a single row to a double row, or between two double row dryer sections. In contrast to the hitherto conventional dryer sections, the fiber web is always supported between the dryer sections.
In a preferred practical embodiment of the dryer section in accordance with the present invention, the material web is transferred in a respective transition zone directly from the drying cylinder of the preceding dryer group by a dryer fabric that is allocated to a succeeding double row dryer group. It is preferred that the material web is received by an upper dryer fabric of the following double row dryer group. The preceding dryer group can again specifically be a single row or a double row dryer group.
The material web can be continuously supported in all transition zones that are provided between two respective dryer groups. In addition, the material or fiber web can, for example, also be continuously supported in a respective transition zone between two single row dryer groups.
It is also advantageous if a suction box is provided for supporting the web transfer in any respective transition zone. In a preferred configuration, the material web travels around a suction roll in a respective transition zone that can, for example, be a suction felt roll and/or a dryer fabric roll. The material web can specifically travel around the suction roll, together with the upper dryer fabric of the following double row dryer group. One of the advantages in doing this is the increased operational safety during threading of the fiber web since, after the transfer to the relating dryer fabric the web can simply be run into the basement, in the event that any problems should arise. This is particularly important at high speeds. The transfer strip can come loose from the dryer fabric. Should this occur, paper shreds fall into the machine basement during this downward directed transfer of the transfer strip from the preceding drying cylinder, where they can no longer interfere with the production process. The paper shreds cannot get into the area above the drying cylinders (dryer felt or dryer fabric run), and cannot therefore, disturb the production process.
A respective suction box and/or a respective suction roll can be provided in a transition zone between any dryer groups, for example even between single row dryer groups.
In an especially cost effective and preferred arrangement, the vacuum in the suction roll is produced via the suction box. This eliminates the expense of having to run the line through the bearing of the suction roll. The shell of the suction roll should be grooved and/or drilled in order to distribute the suction effect across the shell surface that is in contact with the web. It is also possible to connect the suction box with a vacuum source through the interior of the suction roll.
Of particular advantage is the combination of a downward directed web transfer from the drying cylinder of the preceding dryer group by way of the dryer fabric of the following dryer group, a suction roll in the area of the lower rerouting of the dryer fabric, and a suction box for stabilization of the web run between the dryer cylinders and the suction roll.
Particularly advantageous are the transfer edge zones in the suction roll and the suction box in the area where the transfer strip travels during the transfer process. The transfer zones can, for example, be provided on the edge on the operator side of the machine. The transfer zones can be supplied with vacuum, independently of the other zones. This method permits transfer without ropes, thereby simplifying the transfer process as well as improving its safety.